Underground oil or gas drilling operations generally involve drilling a bore using a drill string. The drill string generally includes a drill bit connected to sections of long pipe which form the drill string and extend from the surface of the earth to the bottom of the bore. During the underground drilling operation, information about a position of sensors and the physical property of rocks is generally collected and transmitted to the surface for analysis and control of the drilling operation. A common transmission method used in the industry is based on generating pressure pulses by restricting drilling mud flow.
There are a number of tools which are used for pulse generation in drilling operations. One example is a tool having a rotary pulser construction. Rotary pulsers generally include a fixed stator with passages formed therein for allowing passage of drilling mud flow and a rotating rotor for closing and opening the passages of the stator to generate pressure pulses. With such rotary pulsers it can be difficult to obtain information regarding changes in the pressure of the drilling mud or of conditions in the bore, conditions which may require an adjustment of the generated pressure pulses. Therefore, higher maintenance issues and energy consumption can occur.
Traditional rotary pulsers generally include a motor for driving rotation of the rotor relative to the stator. The mechanical interaction between the motor, gears and/or shafts results in wear of the components over time and high energy consumption. Traditional rotary pulsers also generally do not have the ability to adjust the rotation of the rotor based on system parameters or conditions. Energy can be provided to the motor via a battery, which results in a limitation in the maximum rotational frequency of the rotor based on the power output from the battery. For example, some traditional rotary pulsers can be limited to approximately 4 Hz for rotation of the rotor. If high loads occur during the drilling process and there is a desire to work at a higher speed, a large current input is needed. The limit of current output of batteries (e.g., 5 A) limits the maximum speed of the rotor. Increasing the current output from a battery results in a faster uncharging time of the battery, thereby preventing the necessary work from being performed due to the constant replacement of the battery. The increased amount of uncharging and recharging of the battery can result in a decrease in functionality and effectiveness of the battery, creating further limits on the drilling process. Although generators can be used to power traditional rotary pulsers without incurring the uncharging/recharging issues, the traditional rotary pulsers still do not provide the ability to adjust the rotation of the rotor based on system parameters or conditions.
Signals produced by rotary pulsers can be divided into three types: positive pulse, negative pulse, and continuous wave. Positive pulses can be generated by brief partial or complete closure of the passages of the stator to prevent downward flow of the drilling mud. Negative pulses can be generated by short moments of bypass of the drilling mud through a valve passage. Continuous waves provide a continuous signal in time and amplitude. Continuous wave signals accurately reflect the shape of the wave that propagates in the drilling mud.
Creation of such signals can be performed by a rotary or linear type of mechanism. For example, the main shut-off or closure element for the drilling mud can be either a rotary drive (e.g., a closure element rotates to close the passages and prevent passage of drilling mud therethrough) or a linear translational drive (e.g., a closure element is moved linearly in a direction similar to that of flow of the drilling mud (or perpendicular to the flow of the drilling mud) to block the passage of drilling mud through an orifice).
An actuator can be used to drive the movement of the closure element. The actuator can be electric, hydraulic, mechanical, or a combination thereof. For example, an electric actuator can electrically drive the closure element, a hydraulic actuator can hydraulically drive the closure element, a mechanical actuator can mechanically drive the closure element, and a combination actuator can use two or more of the actuator types to drive the closure element.
Individually, each type of actuator has limitations and disadvantages for drilling operations. For example, as noted above, electric drive has limitations in the amount of power generated, e.g., the power per unit of volume of drive. Therefore, a combination of electric drive with mechanical gearing can be used. However, this combination has the limitations of low speed generation and high wear of the mechanical components. Hydraulic actuators generally require the use of vortex elements. In practice, a combination of electro-hydraulic drive provide a simpler assembly of components and a larger power density as compared to electromechanical drive. For example, the data transfer speed can be between approximately 3-5 bits/second. However, the limitations are caused by the use of the actuator to generate the desired pressure pulses in drilling mud.
Thus, a need exists for rotary pulsers including telemetry systems that adjustably control drilling operations to improve energy consumption and reduce maintenance issues. A need also exists for rotary pulsers including electrohydraulic actuator drives that create positive pulse signals and/or continuous wave signals. A need also exists for rotary pulsers that can be used to create pulse waves of almost any geometry or shape depending on the capabilities of the energy source. A need further exists for rotary pulsers that can be used to vary the form and type of information signal transmission which allows for an increase in the data transmission rate. These and other needs are addressed by the rotary pulsers and associated methods of the present disclosure.